1. Field of the Invention
The present invention relates to an elastomeric bearing installed at an upper girder of a bridge or between upper and lower parts of a building, for supporting a load in a stable manner, and more particularly, to an elastomeric bearing for supporting a high load, which can enhance stability, while supporting a higher load, and which can reduce the construction cost by reducing its own width.
2. Description of the Related Art
A conventional elastomeric bearing 100, as shown in FIG. 7, includes an upper plate 200, a lower plate 300 and an elastomeric pad 110 disposed therebetween. The elastomeric pad 110 includes a body 11 made of rubber and a plurality of reinforcement plates 112 inserted into the body 111 to be parallel in a horizontal direction.
The elastomeric pad 110 is directly installed as a single member so as to allow buckling or sliding while supporting an upper load of a girder or building. Alternatively, occasionally, the elastomeric bearing 100 shown in FIG. 7 is advantageously used in order to control buckling or sliding of the elastomeric pad 110 in a predetermined direction or at a predetermined angle. Here, the directions of movement of the elastomeric pad 110 are controlled by installing stoppers, guides, clamps or the like at the upper plate 200 and the lower plate 300 so as to correspond to each other, thereby suppressing buckling or sliding of the elastomeric pad 110. This technology is known well and a detailed explanation thereof will not be made.
Since the body 111 of the elastomeric pad 110 is made of rubber, buckling or sliding occurs within the elastomeric pad I 10 due to physical properties of rubber at a predetermined angle according to the direction of a load applied. Also, since the elastomeric pad 110 includes a plurality of reinforcement plates 112, excessive deformation due to compression can be prevented. Further, if an excessive horizontal load is applied like in the event of the earthquake, the work energy is turned into the deformation energy of the rubber body 111, thereby reducing a shock due to the horizontal load. Thus, the elastomeric pad 110 must be designed so as to operate properly with an ultimate strength of rubber. Also, the elastomeric pad 110 must accommodate a temporary overload or deformation greater than a design load without being destroyed.
If a load is applied to the conventional elastomeric pad 110, the deformation(expansion) of the body 111 incorporating reinforcement plates 112 is somewhat suppressed. However, the body 111 between the reinforcement plates 112 may undergo expansion in every direction, that is, susceptible to deformation, thereby degrading durability and a load-supporting stress. Thus, there is a limit in improving stability while supporting a high load. Also, since the height of an elastomeric pad is proportional to the moving distance of the upper plate of a bridge, various types of elastomeric pads must be fabricated according to the moving distances of the upper plates of various bridges.
Thus, an elastomeric bearing (or elastomeric pot) shown in FIG. 8 has been proposed and used. According to the proposed elastomeric bearing, an elastomeric bearing 100 includes an upper plate 200, a lower plate 300 having a cylindrical hollow 310, and an elastomeric pad 120. The elastomeric pad 120 includes an elastomeric member 121 made of rubber and seated in the cylindrical hollow 310 of the lower plate 300, a piston 122 inserted into the cylindrical hollow 310 to be elastically supported upwardly by the elastomeric member 121, a sliding plate 123 fixed on the top surface of the piston 122, for allowing smooth sliding of the upper plate 220, and sealing means fixed to the piston 122, for sealing the elastomeric member 121 seated in the cylindrical hollow 310. Here, the sliding plate 123 is generally made of polytetrafluoroethylene (PTFE) resin.
The elastomeric pad 120 cannot be used as a single member in view of its structure and is necessarily used in the elastomeric bearing 100 reinforced with the upper plate 200 and the lower plate 300.
The elastomeric bearing 100 may be embodied in various types as necessary. For example, an omni-directionally movable elastomeric bearing is shown in FIG. 8. In the case of an omni-directionally fixed elastomeric bearing, the sliding plate 123 is removed, and the upper plate 200 and the piston 122 of the elastomeric pad 120 are integrally formed, thereby preventing the upper plate 200 from sliding in every direction, by means of the piston 122 inserted into the cylindrical hollow 310. Also, in the case of a uni-directionally movable elastomeric bearing, guide grooves are formed at the upper plate 200 and/or the piston 122 in one direction, and separate guide pins are inserted into the guide grooves or guide pins are installed at the upper plate 200 or the piston 122 positioned at locations corresponding to the guide grooves, thereby allowing the upper plate 200 to slide in one direction along the guide grooves.
When a vertical load is applied to the elastomeric bearing 100 having the elastomeric pad 120, the piston 122 sways in every direction so that it is buckled in every direction like the elastomeric bearing 100 shown in FIG. 7.
In the elastomeric bearing 100 shown in 8, since the elastomeric member 121 is sealed on the cylindrical hollow 310 of the lower plate 300, a vertical load is applied to the elastomeric bearing 100 so that expansion does not occur even if the elastomeric member 121 is pressed. Therefore, the elastomeric bearing 100 shown in FIG. 8 is safer than the elastomeric bearing 100 having the elastomeric pad 110 shown in FIG. 7, while supporting a higher load.
In the elastomeric bearing 100 shown in FIG. 8, since the cylindrical hollow 310, the elastomeric member 121 and the piston 122 are circular in terms of their mechanical structures, in the case where the size of the elastomeric bearing 100 is increased for the purpose of supporting a higher load, the diameter and depth of the cylindrical hollow 310 and the width of the lower plate 300 having the cylindrical hollow 310 are increased by predetermined increment based on the Hoop""s formula which is well known in the art.
The length of a beam or truss constituting a girder is tensile or elastic due to its tare, external force or a change in the temperature. Thus, in order to support the beam or truss constituting a girder, an appropriate edge distance is required considering safety.
In the case of supporting a beam or truss constituting a girder using the elastomeric bearing, with the elastomeric bearing fixed on the top surface of a bridge pier, in order to secure an appropriate edge distance, a predetermined width of the elastomeric bearing is required. Also, in order to safely support the pier or elastomeric bearing, a predetermined width of the top surface of the pier is required. If the width of the elastomeric bearing for securing an edge distance and the width of the top surface of the pier for supporting the elastomeric bearing are unnecessarily increased, the overall width of the pier must be larger than is designed, which considerably increases the construction cost. Therefore, it is necessary to determine an appropriate width of the elastomeric bearing and an appropriate width of the top surface of the pier, that is, while obtaining an edge distance and ensuring safety.
In the case of supporting a beam or truss using the elastomeric bearing 100 shown in FIG. 8, the elastomeric bearing 100 must have a predetermined size in order to support a sufficiently high load. However, as described above, since the size of the elastomeric bearing 100 is increased, the length and width thereof are uniformly increased. Thus, as the width of the elastomeric bearing 100 becomes greater than a predetermined length for securing the edge distance, an unnecessary increase in the overall width of a pier is unavoidably caused, resulting in a waste of the construction cost, which causes a limitation in use.
Also, in the case of a bridge for vehicles, in particular, for railway vehicles, a dynamic force is applied to a beam of the bridge. Here, an elastomeric bearing for supporting the dynamic force is preferably constructed in view of safety such that buckling occurs in the axial direction of the bridge while suppressing buckling occurring at a right angle with respect to a longitudinal direction, that is, distortion of the beam. However, since the elastomeric pad 110 shown in FIG. 7 and the elastomeric bearing 100 shown in FIG. 8 are configured so as to allow buckling in every direction, a safety problem cannot be avoided.
To solve the above-described problem, it is an object of the present invention to provide an elastomeric bearing for supporting a high load by constricting expansion during compression, for enhancing safety due to unidirectional buckling, and for reducing the construction cost.
To accomplish the above object of the present invention, there is provided an elastomeric bearing for supporting a high load, having an upper plate, a lower plate and an elastomeric pad having a pair of sliding plates on its top surface and disposed between the upper and lower plates, wherein the elastomeric pad comprises: a cylinder member having a plurality of cylindrical hollows, elastomeric members seated on the respective cylindrical hollows of the cylinder member, a plurality of pistons inserted into the respective cylindrical hollows of the cylinder member to hermetically seal the elastomeric members seated thereon, and elasticity reinforcement elements integrally formed with the cylinder member and the plurality of pistons, for accommodating the same, the cylinder member having a plate-shaped body and a plurality of cylinders having cylindrical hollows formed therein, the plurality of cylinders protruding from the bottom of the body.